Offset printing machines are well known in the art and include a master or plate cylinder having a plate for carrying a transferable image thereon and an impression cylinder for carrying paper to receive the image. A blanket cylinder is interposed between the master cylinder and the impression cylinder such that the blanket cylinder moves eccentrically about a first pivot point to make pressure contact with the master cylinder for receiving the image and subsequently moves eccentrically about a second pivot point for making pressure contact with the impression cylinder to transfer the image to the paper. Such a system is disclosed in U.S. Pat. No. 4,691,631.
Two-color offset printing machines are also known and they include a single impression cylinder, two master cylinders and two blanket cylinders. A first blanket cylinder is caused to move eccentrically about a first axis to make contact with a first master cylinder and receive the image therefrom and then move eccentrically about a second pivot point to make contact with the impression cylinder and transfer the first color to the paper on the impression cylinder. The impression cylinder then rotates to the other pair of master and blanket cylinders where the blanket cylinder moves eccentrically into contact with the second master cylinder to receive the second color and subsequently moves eccentrically into contact with the impression cylinder to transfer the second color to the paper. This system is also disclosed in U.S. Pat. No. 4,691,631.
In both single and multi-color such as two color offset printing machines, a predetermined contact pressure must be maintained between the blanket cylinder and the master cylinder and between the blanket cylinder and the impression cylinder. Thus, the mounts for eccentrically supporting the blanket cylinder are rotationally forced against a fixed but adjustable stop which is manually adjusted in the prior art to allow a desired amount of pressure at the contact points between the master and blanket cylinders and between the blanket and impression cylinders, respectively. Adjustment is time-consuming, but readjustment is required for wear and the like as the press is generally set up to print with a relatively fixed thickness of plates, blankets and paper stock. Adjustment, if it is required, is accomplished by varying the thickness of the packing sheets underneath the plate on the master cylinder or paper on the impression cylinder or blanket on the blanket cylinder.
Small sheet-fed presses, in particular, are required to accommodate a wide range of plate and paper stock thicknesses, so such semi-permanent adjustments mentioned above are unusable. If the settings are to be made frequently, then they must be done simply and quickly which is difficult as the adjustment of the actuating means requires that the stop must also be accurately readjusted. Because it is necessary for the eccentrics to rotate freely thereby necessitating some clearance or springiness as in the case of bearings, if rigid stops, such as used in adjusting a web-type press, are not used to rotationally position the eccentrics, there will be a looseness which will allow the printing cylinders to bounce slightly which will be visible in the printing. Wear will obviously increase the looseness. This bouncing of the cylinders is caused by the manner in which they operate. Levers comprise part of a toggle for selectively rotating a first eccentric and an eccentric shaft such that the first eccentric moves against stops which arrest its rotation thus providing exact gap clearance between the blanket cylinder and the master cylinder and thus providing an exact contact pressure. For a significant portion of the revolution of the blanket cylinder and the master cylinder, there is no impression or contact pressure during which time the cylinders tend to move together as there is no resisting force. When the cylinders rotate around to where the printing begins again, an impact occurs which tends to push the cylinders apart. They are eventually restored to their former positions after several reverberations. This ringing of the printing cylinders occurs and is disruptive of proper printing. Additionally, when this occurs between, for instance, the master cylinder and the blanket cylinder, the effect will be felt at the image transfer point between the blanket cylinder and the impression cylinder. It is an effect commonly referred to as streaking.
Although it is not possible to totally eliminate this effect, it may be minimized to an acceptable level if the blanket cylinder throw-off controls are designed to be very rigid and the forces which restrain the eccentrics are caused to be directed in essentially the same direction as the impression forces and to be several times as great in magnitude. These forces consist of the force to move the sleeve toggle that causes the first eccentric movement of the blanket cylinder and the resisting force from the stop mechanism. The vector sum of these two forces must be greater than and fall between the force vector of the contact between the master cylinder and blanket cylinder and between the blanket cylinder and the impression cylinder. In such case, even though a certain amount of looseness is required to allow for the eccentrics be free to turn, the eccentrics are pressed against their mounts in essentially the same direction as the impression pressures and any tendency for the eccentrics to move within their mounts is virtually eliminated. Thus, it is seen that the adjustment of the eccentric actuating means and the adjustment of the stop require a balancing of forces. If the stop force is too great, the toggle lever cannot be locked and, if it is too little, the eccentric actuating means will be loose and there will be streaking and slurring of the printed image. On presses where impression pressure adjustments are seldom made, as in the web-type press, this manual adjustment can readily be accommodated. However, on presses requiring frequent changes in paper and plate thickness, protracted adjustment procedures are undesirable.
In the present invention, a sleeve actuator is mounted in the frame side walls of the printing mechanism to cause the blanket cylinder to move eccentrically into and out of pressure contact with the master cylinder. A stub shaft is eccentrically mounted in the sleeve and rotatably holds the blanket cylinder. The stub shaft is rotated to cause the blanket cylinder to move eccentrically into and out of pressure contact with the impression cylinder. Pneumatic cylinders are connected to levers which comprise part of a toggle for selectively rotating the sleeve actuator and the eccentric stub shaft. The sleeve moves against stops which arrest its rotation, thus providing an exact gap between the blanket cylinder and the master cylinder and causing an exact impression pressure. The toggle lever for moving the sleeve and thus the blanket cylinder into and out of pressure contact with the master cylinder is mounted on an eccentric bushing. The eccentric bushing is rotatably adjustable to change the pivot point of the toggle lever, which changes the amount of movement of the sleeve actuator and thus the amount of movement of the blanket cylinder toward and away from the master cylinder. In this manner, the contact pressure is adjusted as desired in a simple and efficient manner.
In addition, the pivot point of the second toggle lever which rotates the eccentric stub shaft is also adjustable so that the amount of rotation of the stub shaft can be changed, thus changing the amount of movement of the blanket cylinder towards and away from the impression cylinder to maintain a constant or predetermined contact pressure.
In addition, the stop for the sleeve actuator is mounted on the sleeve itself and a cam is mounted on the shaft for rotatably adjusting the eccentric bushing. An arm is pivotally mounted for connection between the cam and the stop so that when the pivot point of the toggle lever moving the sleeve is adjusted by rotating the eccentric bushing, the cam is also adjusted so that the contact of the stop with the arm is simultaneously adjusted. Thus, adjustment of the toggle link is automatically coordinated with an adjustment of the stop. The throw-off toggle levers are designed to be very rigid and cause the forces which restrain the eccentrics to be directed in essentially the same direction as the impression forces and several times as great in magnitude. Therefore, any tendency for the blanket cylinder to bounce against either the master cylinder or the impression cylinder is minimized, thus minimizing streaking and slurring of the printed image.
In the present invention, when a two-color offset printing machine is utilized, the first adjustment arms for each of the toggle levers that move the sleeve actuators are coupled by a first rod to each other. The rod is threadedly attached at each end to the first adjustment arms and has a wheel rotatably attached to the rod for rotating the rod. Thus, rotation of the rod in a first direction moves the first adjustment arms of each of the sleeve actuators in opposite directions to simultaneously adjust the pivot points of the toggle levers of each of the sleeves, thus simultaneously adjusting the contact pressure between each of the blanket cylinders and its corresponding master cylinder. A digital counter is coupled to the rod such that rotation of the rod in either direction causes the counter to change its count to provide an indication of the movement of each of the first adjustment arms by rotation of the rod.
A second rod is coupled to each of the second adjustment arms for the eccentric stub shafts such that rotation of the rod in either direction causes the second adjustment arms to move simultaneously to change the rotation of the eccentric stub shafts and thereby change the movement of the blanket cylinder toward and away from the impression cylinder to maintain a substantially constant contact pressure. Again, a digital counter is coupled to the second rod to digitally indicate the amount of movement of the second adjustment arms and thus indicate the change in contact pressure between each blanket cylinder and the impression cylinder.
Thus, one of the objects of the present invention is to provide an offset printing machine in which the blanket cylinder moves eccentrically about a first pivot point to contact the master cylinder and eccentrically about a second pivot point to contact the impression cylinder and wherein each of the first and second pivot points is easily adjustable to maintain a predetermined contact pressure between the blanket cylinder and the master cylinder and between the blanket cylinder and the impression cylinder.
It is also an object of the present invention to change the contact pressure between the blanket cylinder and the master cylinder by rotating a first rod in first and second directions.
It is yet another object of the present invention to change the contact pressure between the blanket cylinder and the master cylinder by rotating a first adjustment arm to change the pivot point of a toggle lever that moves the sleeve actuator to adjust the first pivot point about which the blanket cylinder moves eccentrically.
It is also an object of the present invention to provide a rigid stop mechanism for limiting the movement of the blanket cylinder toward the master cylinder.
It is still another object of the present invention to automatically adjust the rigid stop whenever the first pivot point is adjusted so as to maintain the desired contact pressure between the blanket cylinder and the master cylinder.
It is also an object of the present invention to provide a digital counter for digitally indicating the amount of adjustment of the first pivot point and thus the movement of the blanket cylinder toward and away from the master cylinder.
It is yet another object of the present invention to provide a second adjustment arm coupled to an eccentric stub shaft to adjust the second pivot point of the blanket cylinder thereby adjusting the amount of movement of the blanket cylinder toward and away from the impression cylinder.
It is also an object of the present invention to provide a second rotatable rod coupled to the second adjustment arm for moving the second pivot point by adjusting the pivot point of a second toggle lever that rotates the eccentric stub shaft, thereby changing the amount of movement of the blanket cylinder toward and away from the impression cylinder.
It is still another object of the present invention to provide an adjustment wheel coupled to the second rotatable shaft to vary the amount of movement of the second adjustment arm and thus adjust the amount of movement of the blanket cylinder toward and away from the impression cylinder.
It is yet another object of the present invention to provide a second digital counter that is coupled to the second rotatable rod to digitally indicate the amount of movement of the second adjustment arm and thus indicate the relative change in movement of the blanket cylinder toward and away from the impression cylinder.
It is also an object of the present invention to provide a multi-color offset printing machine which has a first rod for simultaneously adjusting the first pivot points of both blanket cylinders simultaneously to adjust the pressure contact simultaneously between each of the blanket cylinders and their respective master cylinders.
It is also an object of the present invention to provide a multi-color offset printing machine having a second rod simultaneously adjusting the second pivot point of both of the blanket cylinders to simultaneously adjust the amount of movement of each blanket cylinder toward and away from the impression cylinder.
It is still another object of the present invention to coordinate the adjustment of the impression forces with the automatic adjustment of a rigid stop mechanism to cause a resultant force vector to be greater than and fall between the force vector representing the contact pressure between the master cylinder and the blanket cylinder and the contact pressure between the impression cylinder and the blanket cylinder to essentially eliminate the tendency for the eccentrics to move in their mounts.